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80 HPFP: Recent Advances in Insects and Other Arthropods Vol. 1 Karel Sláma In addition to certain favorite species, like a hawkmoth (M. sexta), American cockroach (P. americana) or a mealworm (Tenebrio molitor), further reports on the cardioactive effects of neuropeptides came from a very competitive field of biological research, the heart of the fruitfly (D. melanogaster). Here, the cardioactive properties of neuropeptides were tested by optoelectronic, real in vivo recording methods.The effects were expressed as percentages of relative heartbeat increase within a 3 min period after injection of the neuropeptides [25-27] (see below). It was axiomatically believed that the heart of D. melanogaster, unlike the human heart, was neurogenic and, therefore, it should be a target of the neuropeptides (see also [28- 29]). Similar theoretical calculations underlined the in vitro bioassays for cardiostimulating properties of natural and synthetic derivatives of proctolin [32-34] and other synthetically prepared neuropeptides [35-36 review]. In all these investigations, the principal criterion of positive cardiostimulating action was the immediate chronotropic effects which indicate, in other words, increased rate of heartbeat. From the described literature survey one might get the impression that most natural or synthetic neuropeptides in insects should be for some reason cardioactive. In fact, researchers have failed to ask whether this accepted "cardioactive" theory has some kind of physiological justification. Or, why the neuropeptides, synthesized by rather slow and complicated biosynthetic routes within the brain, should then compete for heartbeat control with the trivial, low molecular metabolic feed-back factors. The reported "cardiostimulating" action of insect neuropeptides also has no counterpart in animal physiology and in human medicine a cardiostimulating peptide does not exist. Finally, the recently invented, in vivo electrocardiographic methods, developed specifically for monitoring the functions of insect heart [1, 6, 7, 37-40], have failed to confirm the cardiostimulating claims. Let us briefly describe the new, in vivo obtained cardiological results and compare them with the old, in vitro reports on the cardiostimulating properties of insect neuropeptides in the most investigated species, M. sexta, P. americana, T. molitor and D. melanogaster. NEUROPEPTIDES AND THE HEART OF MANDUCA SEXTA In accordance with the old concepts of nervous or neurohormonal regulation of insect heartbeat [14], it was assumed some 20-years ago that the heart of M. sexta was ´modulated in vivo by a number of neurally derived peptides [18, 19]. And, as a matter of fact, neuropeptides isolated from the nervous system indeed stimulated the heartbeat rate when subjected to simple bioassay methods [18]. The idea of neurogenic regulation of heartbeat in M. sexta was generally accepted by other authors [16, 30] who claimed to discover a neurogenic pacemaker cardiac center among the neurons of the terminal ganglionic mass at the end of the abdomen [16]. Heartbeat patterns of M. sexta were investigated earlier using the method of impedance conversion [43]. This invasive method used wire electrodes implanted into the body. It had low sensitivity and usually collected all kinds of artifacts associated with the movements of other visceral or somatic organs. Due to this, the pupal heartbeat patterns of M. sexta were considered to be quite irregular or "erratic" [43]. A few years later, after the invention of touch-free, noninvasive, in vivo electrocardiographic methods [1, 5, 7] it appeared, however, that the pattern of pupal heartbeat in M. sexta was absolutely regular and well reproducible, especially during the several months of pupal diapause. This statement is documented in Fig. 1 which shows an absolutely regular pattern of heartbeat reversal revealed by optocardiographic recordings from the base and the end of the pupal abdomen [1]. The method enables prolonged monitoring of individual systolic contractions of the heart from a distance of 7 mm. In principle, there is a beam of 5 kHz pulse-light, which is focused to 0.3mm 2 epidermal area in the middle of the abdominal tergites, above the pericardial region. The light modified by movements of the heart is reflected back into the instrument and recorded after decoding and amplification [1]. The method enables the precise determination of cardiostimulating effects after injections of neuropeptides, including alternation of faster (anterograde) and much slower (retorograde) directions of the heartbeat (Fig. 1). The most essential condition of all these physiological experiments depends on control recordings using injections of Ringer or water solutions alone. Underscoring or neglecting satisfactory control experiments can lead to the creation of false positive judgements and myths about the "potent cardioaccelerating" properties of insect neuropeptides.
94 Hemolymph Proteins and Functional Peptides: Recent Advances in Insects and Other Arthropods Vol. 1, 2012, 94-110 Muhammad Tufail and Makio Takeda (Eds) All rights reserved-© 2012 Bentham Science Publishers CHAPTER 6 Structures and Functions of Insect Midgut: The Regulatory Mechanisms by Peptides, Proteins and Related Compounds Makio Takeda * Graduate School of Agricultural Science, Kobe University, 1-1Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan Abstract: The midgut is an important organ for insects not only because it occupies a large space in their hemocoel, or because it is a major part of the digestive tract; it also plays critical roles in other physiological regulation such as metabolism, immune response, homeostasis of electrolytes, osmotic pressure, circulation and more. Therefore disturbance of these functions could provide a target and strategy for future pest management practice. Entry of entomopathogenic microorganisms and penetration of pesticides are through this route, and Plasmodium penetrating through the peritrophic membrane of Anopheline mosquitoes is a crucial issue for malaria control. The midgut is a complex organ that undergoes a gross transformation at metamorphosis to support different feeding habits at different developmental stages. It consists of epithelium and basal lamina with endodermal and mesodermal origins, respectively and the latter is innervated, i.e., an ectodermal element. We have not yet reached complete elucidation and understanding of the mechanism of embryonic formation of the organ, the metamorphosis and the regulatory mechanisms for a variety of midgut house-hold physiological functions. Another complexity comes from the unusual extent of variabilities that occur in general morphology, egg size/yolk content, feeding habit, mode of metamorphosis, or kinds of stresses or symbiotic associations that may occur in various orders of insects. We do not know whether the Drosophila model that provides important knowledge concerning embryonic formation is applicable to other insects. This review focuses on functions of developmental genes, endocrine agents, and local secretagogues, that control regulatory mechanisms, particularly peptides secreted from epithelial paraneurons as well as growth factors and differentiation factors synthesized by non-paraneuronal midgut cells such as columnar cells, goblet cells, perhaps trachea, hemocytes or muscles or extramidgut tissues such as the fat body. Stress conditions and metamorphosis, epithelial-mesenchymal interactions and behavior of adhesion molecules should be included here but currently this aspect has received little attention. Keywords: Brain-gut peptides, paraneurons, growth factors, differentiation factors, metamorphosis, gut contraction, digestion, metabolism, 20-hydroxyecdysone, bombyxin, serotonin, apoptosis, stem cell. INTRODUCTION Hormones are circulating agents produced by endocrine glands that control physiological functions in sites remote from the site of production. The nervous system also produces chemical signals with structures similar to hormones and secretes them not only to synaptic junctions but also to the general circulation. For example, adrenalin is a hormone but is also released into synaptic junctions. Ernst and Bertha Scharrer [1] unified endocrinological and neurological traditions by the integrating concept of “neurosecretion”. Neurons secrete conventional neurotransmitters (synaptocrinia), neuropeptides (synamptocrinia, paracrinia and endocrinia) or autocrine agents such as nerve growth factor (autocrinia). Confusions, however still remain; some non-neural tissues can produce “neuropeptides”. This was originally found in mammalian intestines, thymus, placenta etc., and the same conditions are found in insects. Some like Pearse [2] assumed that these “endocrine cells” must have an ectodermal origin and have migrated from the neural crest to the epithelium, the APUD hypothesis (Amine Precursor-Uptake- Decarboxylation). However, currently the midgut “endocrine cells,” at least in insects, are considered as having their origin different from neural tissue [3, 4]. *Address correspondence to Makio Takeda: Graduate School of Agricultural Science, Kobe University, 1-1Rokkodai-cho, Nadaku, Kobe, 657-8501, Japan; Ph/Fax; +81-78-803-5870; Email: mtakeda@kobe-u.ac.jp
Page 2 and 3: Hemolymph Proteins and Functional P
Page 4 and 5: CONTENTS Foreword i Preface ii List
Page 6 and 7: ii PREFACE The aim of this eBook
Page 8 and 9: iv Giancarlo Lopez-Martinez Departm
Page 12 and 13: Hemolymph Lipoproteins: Role in Ins
Page 14 and 15: Adipokinetic Hormones and Their Rol
Page 16 and 17: 32 Hemolymph Proteins and Functiona
Page 18 and 19: 34 HPFP: Recent Advances in Insects
Page 20 and 21: Immune Response of Insects and Crus
Page 22 and 23: 78 Hemolymph Proteins and Functiona
Page 26 and 27: Structures and Functions of Insect
Page 30 and 31: Neurohormones and Second Messengers
Page 32 and 33: Role of Conventional and Unconventi
Page 36 and 37: Insulin-Related Peptides in Insects
Page 38 and 39: ENF Peptides HPFP: Recent Advances

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